1. Field of the Invention
The present invention relates to a multiple-light cold-cathode tube lighting device used for a display device.
2. Description of the Related Art
In general, a liquid crystal display panel having a built-in backlight is used for a display portion of a computer or the like, and a plurality of cold-cathode tubes are used as the backlight of this liquid crystal display panel in order to ensure brightness and to prevent unevenness of luminous intensity.
In the multiple-light cold-cathode tubes, since a flicker is generated by lighting frequency fluctuation, it is necessary that an oscillating circuit is made common to the cold-cathode tubes to establish mutual synchronization of them and to suppress the flicker.
FIGS. 3 and 4 show conventional multiple-light lighting devices.
FIG. 3 is a circuit diagram showing a conventional multiple-light lighting device, which is disclosed in Japanese Patent Laid-Open No. 298995/1992.
In FIG. 3, reference numerals 1 and 2 designate inverter circuits, respectively. Reference characters Q1, Q2, Q3 and Q4 designate transistors; C1, C2, C3 and C4, capacitors; T1 and T2, transformers; and Nf1, a base winding of the transformer T1. Reference character L1 designates a choke coil; and CCFL1 and CCFL2, cold-cathode tubes.
The multiple-light lighting device of FIG. 3 is constituted by the pair of the inverter circuits 1 and 2, the base winding Nf1 of the transformer T1 of the inverter circuit 1 is inputted to the respective oscillating circuits, so that lighting frequencies of the respective cold-cathode tubes CCFL1 and CCFL2 are made identical to each other.
FIG. 4 is a circuit diagram showing a conventional multiple-light lighting device.
In FIG. 4, reference numeral 1 designates an inverter circuit; Q1 and Q2, transistors; C1, C2 and C3, capacitors; and T1 and T2, transformers. Reference character L1 designates a choke coil; and CCFL1 and CCFL2, cold-cathode tubes.
The multiple-light lighting device of FIG. 4 is constituted by the inverter circuit including the choke coil L1, and the two output transformers T1 and T2. By connecting the transformer T1 and the transformer T2 of the inverter circuit in parallel, the same lighting frequency is held in common, and output synchronization is established.
Although all of the plurality of cold-cathode tubes can be synchronized by the foregoing technique, there has been a problem that it can not satisfy a light control system further diversified in future.
The present invention has been made to solve the foregoing problem, and an object of the invention is to provide a multiple-light cold-cathode tube lighting device in which a plurality of cold-cathode tubes are mutually synchronized to prevent a flicker, while they can be independently subjected to light control.
A multiple-light cold-cathode tube lighting device of the present invention includes a first inverter constituted by a first amplifying circuit having an oscillating function and first transformers connected to the first amplifying circuit and including a first base winding, first cold-cathode tubes connected to output ends of the first transformers, a second inverter constituted by a second amplifying circuit having an oscillating function and second transformers connected to the second amplifying circuit and including a second base winding, and second cold-cathode tubes connected to output ends of the second transformers, and one of the first base winding of the first inverter and the second base winding of the second inverter is selected and is connected to the first amplifying circuit and the second amplifying circuit.
Besides, the first amplifying circuit and the second amplifying circuit are respectively connected to power sources through switches, and lighting of the first cold-cathode tubes and lighting of the second cold-cathode tubes are individually controlled by controlling the switches.